As one of the methods for performing a detoxification treatment on a contaminated liquid containing harmful substances such as organic contaminants, there exists a treatment making use of biological activity, but the processing speed thereof is slow because it depends on a biochemical reaction by a microorganism, in addition, a microorganism tank for decomposing the harmful substances is needed, and the operation/maintenance of the microorganism tank needs much attention and experience. The decomposition of a harmful substance such as an organic contaminant by a microorganism is generally performed through oxidation of the harmful substance in an aerobic atmosphere, but in the removal of ammonia being a malodorous component by a digesting bacterium, there remains a problem such as adjustment of pH after the oxidation of ammonia, or disposal of nitric acid. On the other hand, as one of the methods for performing a detoxification treatment on water containing harmful substances including malodorous components such as various kinds of COD components and ammonia in low concentrations, there exists a method for performing an oxidative decomposition treatment with ozone, and various proposals have been made in order to improve the efficiency of the treatment. For example, an oxidation treatment method with a mixed solution containing: a water-soluble oxidizing agent such as an oxygen-containing halogenated compound or hydrogen peroxide; and dissolved ozone has been attempted (Patent Literatures 1 and 2), but the rate of reaction between a harmful substance in a low concentration and the water-soluble oxidizing agent or the mixed solution containing the water-soluble oxidizing agent and dissolved ozone is not so large, and therefore the single use of the method has not been put into practical use yet. However, autolysis progresses in the mixed solution containing the water-soluble oxidizing agent and dissolved ozone, and therefore there is a small risk that the water-soluble oxidizing agent and dissolved ozone are left in a treated liquid to affect a human body, so that the mixed solution is anticipated to expand the field of application as a clean treating agent further in future, and when the mixed solution can be utilized as an oxidizing agent for treating a harmful substance-containing liquid, a method using the mixed solution is expected as a greatly effective treatment method.
In addition, with respect to the oxidative decomposition treatment of a harmful substance with dissolved ozone, there are proposals on a high silica adsorbent adsorbing a harmful substance and adsorbing ozone for the purpose of performing the oxidative decomposition treatment efficiently (Patent Literatures 3 and 4). Further, in recent years, there have been proposed a method and an apparatus for producing ozone water directly through electrolysis in place of a method for obtaining dissolved ozone through dissolution of an ozone gas, and it is described that the obtained ozone water can be utilized for decomposition of organic chlorine compounds containing dioxin or disposal of a waste liquid containing dioxin (Patent Literatures 5 and 6).